Change Docker image to fix broken builds

Apparently jekyll/builder image is now broken, using the ruby:alpine
image works instead.

.gitlab-ci.yml

-image: jekyll/builder
+image: ruby:alpine
 
 stages:
   - deploy
@@ -7,15 +7,20 @@ variables:
   JEKYLL_ENV: production
   LC_ALL: C.UTF-8
   GIT_SUBMODULE_STRATEGY: recursive
-  BUNDLE_USER_HOME: ./bundle
 
 # Build is in `before_script` because it's the same for both deployments
 before_script:
+  - apk add build-base libressl git bash
+  - id
+  - ls -lah /usr/gem && true
+  - mkdir -p /usr/gem/cache
+  - ls -lah /usr/gem && true
+  - ls -lah /usr/gem/cache
   - apk add npm
   - npm install
   - bundle install
   - ./scripts/ci_fix_baseurl.sh
-  - jekyll build -d public
+  - jekyll build -d public | grep -v 'Using the last argument as keyword parameters is deprecated'
   - ./scripts/purgecss.sh public
   - ./scripts/minifycssjs.sh public
   - ./scripts/add_mailinglist_symlink.sh public